1. Field of the Invention
This invention relates to reciprocating aircraft engines that may be adapted to accept either a controllable pitch, constant speed propeller or a fixed pitch propeller.
More particularly, this invention relates to a reciprocating aircraft engine of the type that supplies oil under pressure to a controllable pitch, constant speed propeller through a hollow crankshaft adjacent the propeller.
2. Description of the Prior Art
Aircraft engines of the type that supply oil under pressure through a hollow front portion of a crankshaft for manipulation of a controllable pitch propeller such as a specific series of lycoming engines manufactured by AVCO LYCOMING DIVISION, Williamsport, PA., provide a Welch-type expansion plug that is positioned in the rear of the hollow front section of the crankshaft if it is desired to install a fixed pitch propeller. To be more specific, a mounting pad is provided, for example, ahead of the number one cylinder in the front of the right crankshaft half of the 0-235-C and 0-290-D that is intended for the installation of a hydraulic valve to actuate a controllable pitch prop. This valve allows engine oil, under pressure, to flow through the hollow crankshaft to the blade rotating mechanism of the propeller. When the valve is closed, the valve halts the oil flow and opens a divertive passage which permits residual oil in the crankshaft and propeller hub assembly to return to the oil sump. The Welch-type expansion plug blocks off this source of oil under pressure within the crankshaft and a fixed propeller may then be installed. These expansion plugs have been known to fail and complete loss of oil from the engine usually means a damaged engine or worse, a forced landing accident.
The present invention prevents a catastrophic loss of oil due to the failure of this expansion plug by providing a safety backup seal device that will retain any oil escaping passed the expansion plug.